Dc/dc converter

ABSTRACT

In a non-isolated DC/DC converter, a reference potential for a low-side pre-driver which drives a gate of a low-side MOSFET is applied from a portion except for a main circuit passing through a high-side MOSFET and the low-side MOSFET so that a parasitic inductance between a source of the low-side MOSFET and the pre-driver is increased without increasing the sum of parasitic inductances in the main circuit and negative potential driving of the gate of the low-side MOSFET can be performed and a self turn-on phenomenon can be prevented without adding any member and changing drive system.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority from Japanese Patent ApplicationNo. JP 2006-046171 filed on Feb. 23, 2006, the content of which ishereby incorporated by reference into this application.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a technique for a non-isolated DC/DCconverter, and in particular to a technique effectively applied to acircuit system and a mounting system which can prevent a self turn-onphenomenon without adding any new member or changing a driving system.

BACKGROUND OF THE INVENTION

For example, a non-isolated DC/DC converter used in power source circuitfor a desktop PC, a notebook PC, a game machine, or the like is in atrend of large current use and high frequency use according to demandfor large current use in a CPU (Central Processing Unit) or an MPU(Micro Processing Unit) or demand for size reduction of a choke coil oran input/output capacitor which is a passive part. The DC/DC converteris composed of a high-side switch and a low-side switch, where a powerMOSFET is used in each of the switches.

The switches are alternately turned ON/OFF to perform voltage conversionwhile synchronizing the high-side and low-side switches with each other.The high-side switch is a switch for controlling the DC/DC converter andthe low-side switch is a switch for synchronization and rectification.

A recent DC/DC converter is in a trend for advance to thesystem-in-package obtained by packaging a high-side switch, a low-sideswitch, and a driver IC for driving the switches in one package in orderto reduce parasitic inductances among chips and satisfy high-speedresponse and size reduction.

FIG. 10 is a circuit diagram of a DC/DC converter using a conventionalsystem-in-package. A system-in-package 1 comprises a high-side MOSFET 2,a low-side MOSFET 3, and pre-drivers 4 and 5 which drive the respectiveMOSFETs. Here, the pre-drivers 4 and 5 are formed in a driver IC 6 asone chip, and three chips of the high-side MOSFET 2, the low-side MOSFET3, and the driver IC 6 are mounted in one package.

An operation principle and respective constituent elements of a DC/DCconverter using the system-in-package will be explained. The pre-drivers4 and 5 drive gates of the high-side MOSFET 2 and the low-side MOSFET 3via wires 7 and 9 according to input of a PWM signal from a PWMcontroller 11. Source potentials of the high-side MOSFET 2 and thelow-side MOSFET 3 are inputted to the pre-drivers 4 and 5 via wires 8and 10, and respective gate voltages thereof are applied based upon thesource potentials. A voltage (VIN) applied to an input terminal 25 viaan input capacitor 14 is converted to a desired voltage according to aratio of an ON period between the high-side MOSFET 2 and the low-sideMOSFET 3 to be outputted to an output terminal 26. The outputted voltageis smoothed by a choke coil 13 and an output capacitor 12 so that anoutput voltage (VOUT) is outputted. A power ground terminal 27 connectedto a power ground 29 and a logic ground terminal 28 connected to a logicground 30 are provided, respectively.

FIG. 11 is a diagram showing a configuration example of asystem-in-package for the conventional DC/DC converter (for example, seeJapanese Patent Application Laid-Open Publication No. 2004-342735(Patent Document 1)). As the package, a QFN (Quad Flat Non-leadedpackage) is used, which is one of non-leaded surface-mounted packages. Atub of the package is divided to three tabs 15, 16, and 17. Thehigh-side MOSFET 2, the low-side MOSFET 3, and the driver IC 6 aremounted on these tabs, respectively. Source pads 18 and a gate pad 19are provided on the high-side MOSFET 2 and they are connected to thedriver IC 6 via wires 7 and 8. The high-side MOSFET 2 is connected tothe low-side MOSFET 3 via a wire 23 and the tab 16. Source pads 20 and22, and a gate pad 21 are provided on the low-side MOSFET 3, and thelow-side MOSFET 3 is connected to the driver IC 6 via wires 9 and 10.The low-side MOSFET 3 is connected to a power ground terminal 27 viawires 24. The tab 17 mounted with the driver IC 6 is connected to alogic ground 30 via logic ground terminals 28.

Next, influence of parasitic inductance in a main circuit will beexplained. FIG. 12 is a circuit diagram showing a portion of circuitconfiguration of the conventional DC/DC converter, where L1 to L6 denoteparasitic inductances in a main circuit. Here, L1 represents a parasiticinductance between an input power source (Vin) and a drain of thehigh-side MOSFET 2, namely, the sum of a wire inductance of a portion ofa printed circuit board extending from the input capacitor 14 to theinput terminal 25 of the system-in-package and a parasitic inductance ofthe tub 15 mounted with the high-side MOSFET 3. L2 represents aparasitic inductance between the source of the high-side MOSFET 2 and areference potential of the pre-driver 4, namely, a parasitic inductanceof the source electrode of the high-side MOSFET 2. L3 represents aparasitic inductance between the source of the high-side MOSFET 2 andthe output terminal 26, namely, a parasitic inductance of a wire (wire23) of the source of the high-side MOSFET 2. L4 represents a parasiticinductance between the output terminal 26 and a drain of a low-sideMOSFET 3, namely, a parasitic inductance of the tab 16 mounted with thelow-side MOSFET 3. L5 represents a parasitic inductance between a sourceof the low-side MOSFET 3 and a reference potential of the pre-driver 5,namely, a parasitic inductance of the source electrode of the low-sideMOSFET 3. L6 represents a parasitic inductance between the source of thelow-side MOSFET 3 and a power ground 29, namely, the sum of a parasiticinductance of a wire (wire 24) of the source of the low-side MOSFET 3and a wire inductance of a portion of the printed circuit boardextending from a power ground terminal 27 of the system-in-package 1 tothe input capacitor 14.

Conventionally, it is known that reduction of the sum (L1+L2+ . . . L6)of inductances in the main circuit or reduction of the parasiticinductance L2 between the high-side MOSFET 2 and the reference potentialof the pre-driver 4 is effective for reduction of loss in the DC/DCconverter.

In the system-in-package, since the high-side MOSFET 2 and the low-sideMOSFET 3 are packaged in one package, the sum of the inductances in themain circuit can be reduced, and since the reference potential of thepre-driver 4 is applied from the source electrode of the high-sideMOSFET 2 via a wire (wire 8), L2 eventually contains only the parasiticinductance of the source electrode so that L2 can be reducedconsiderably.

However, such a problem as a self turn-on phenomenon occurs in the DC/DCconverter. The self turn-on phenomenon means a phenomenon that, when thehigh-side MOSFET is turned ON in an OFF state of the low-side MOSFET, adrain voltage of the low-side MOSFET rises, a charging current flowsbetween the gate and the source of the low-side MOSFET via a feedbackcapacity between the gate and the drain of the low-side MOSFET accordingto the voltage change, and a gate voltage of the low-side MOSFET risesto exceed a threshold voltage, thereby causing erroneous turn-on of thelow-side MOSFET.

FIG. 13 is a graph showing a calculation result of a voltage Vgs betweenthe gate and the source of the low-side MOSFET. As shown in FIG. 13, itis understood that, after the low-side MOSFET is turned OFF, the gatevoltage of the low-side MOSFET rises according to turning-ON of thehigh-side MOSFET. When the self turn-on phenomenon occurs, a largefeed-through current flows from the high-side MOSFET to the low-sideMOSFET so that conversion efficiency lowers largely. As an actuallow-side MOSFET, a MOSFET having a high threshold voltage to a certainextent must be used so as not to cause the self turn-on phenomenon,which results in such a problem that high efficiency can not be achieveddue to increase in conduction loss.

As a technique for preventing the self turn-on phenomenon, a techniquewhere, even if a gate voltage of a low-side switch rises, the gatevoltage does not exceeds a threshold voltage to be capable of preventingthe self turn-on by driving the gate voltage of the low-side switch at anegative potential has been proposed, for example, in Japanese PatentApplication Laid-Open Publication No. 2004-15974 (Patent Document 2). Atechnique where an auxiliary switch is provided between a gate and asource of a low-side MOSFET and the gate and the source areshort-circuited to prevent rising of a gate voltage by making theauxiliary switch conductive at a rising time of a gate voltage of alow-side switch has been proposed in Japanese patent Applicationlaid-Open Publication No. 2002-290224 (Patent Document 3).

SUMMARY OF THE INVENTION

However, since the technique described in Patent Document 2 or PatentDocument 3 requires a circuit for generating a negative potential or anauxiliary switch additionally to prevent self turn-on phenomenon, such aproblem arises that an additional member or change of a drive system isrequired.

In view of these circumstances, the present invention has been made forsolving the above problems and an object thereof is to provide a circuitsystem and a mounting system where a self turn-on phenomenon can beprevented in a non-isolated DC/DC converter, particularly, asystem-in-package for a DC/DC converter without newly adding a member orchanging a drive system.

The above and other objects and novel characteristics of the presentinvention will be apparent from the description of this specificationand the accompanying drawings.

The typical ones of the inventions disclosed in this application will bebriefly described as follows.

The present invention is applied to a non-isolated DC/DC converterhaving a high-side switch, a low-side switch, a high-side pre-driver fordriving the high-side switch, and a low-side pre-driver for driving thelow-side switch, where a reference potential for the low-side pre-driverfor driving the gate of the low-side switch is applied from a circuitexcept for a main circuit passing through the high-side switch and thelow-side switch.

The present invention is applied to a non-isolated DC/DC converterhaving a system-in-package obtained by packaging a high-side switch, alow-side switch, and a driver IC where a high-side pre-driver fordriving the high-side switch and a low-side pre-driver for driving thelow-side switch are packaged in one chip in one package, which has afeature similar to that of the DC/DC converter described above.

The effects obtained by typical aspects of the present invention will bebriefly described below.

According to the present invention, a self turn-on phenomenon can beprevented without adding any new member or changing a driving system,and loss reduction in a system can be achieved in a non-isolated DC/DCconverter, particularly, a system-in-package for a DC/DC converter.

BRIEF DESCRIPTIONS OF THE DRAWINGS

FIG. 1 is a circuit diagram showing a DC/DC converter using asystem-in-package according to a first embodiment of the presentinvention;

FIG. 2 is a diagram showing parasitic inductances in a main circuit inthe DC/DC converter according to the first embodiment of the presentinvention;

FIG. 3 is a graph showing a calculation result of a voltage Vgs betweena gate and a source of a low-side MOSFET for explaining an effect ofpreventing self turn-on in the DC/DC converter according to the firstembodiment of the present invention;

FIG. 4 is a diagram showing a configuration example of asystem-in-package in the DC/DC converter according to the firstembodiment of the present invention;

FIG. 5 is a diagram showing another configuration example of thesystem-in-package in the DC/DC converter according to the firstembodiment of the present invention;

FIG. 6 is a circuit diagram showing a DC/DC converter using a discretedevice according to a second embodiment of the present invention;

FIG. 7 is a diagram showing one example of a wiring pattern on a printedcircuit board of the DC/DC converter of the second embodiment of thepresent invention;

FIG. 8 is a circuit diagram showing a DC/DC converter in which anauxiliary Schottky barrier diode is built-in according to a thirdembodiment of the present invention;

FIG. 9 is a diagram showing one example of a sectional structure of alow-side MOSFET in which the auxiliary Schottky barrier diode isbuilt-in in the DC/DC converter of the third embodiment of the presentinvention;

FIG. 10 is a circuit diagram showing a conventional DC/DC converterusing a system-in-package;

FIG. 11 is a diagram showing a configuration example of asystem-in-package in the conventional DC/DC converter;

FIG. 12 is a diagram showing parasitic inductances in a main circuit inthe conventional DC/DC converter;

FIG. 13 is a diagram showing a calculation result of a voltage Vgsbetween a gate and a source in a low-side MOSFET for explaining a selfturn-on phenomenon in the conventional DC/DC converter;

FIG. 14A is a diagram showing influence of parasitic inductances when aself turn-on phenomenon occurred in the conventional DC/DC converter;

FIG. 14B is a diagram showing influence of parasitic inductances whenthe self turn-on phenomenon occurred in the conventional DC/DCconverter; and

FIG. 15 is a diagram showing one example of a wiring pattern on aprinted circuit board in a conventional DC/DC converter using a discretedevice.

DESCRIPTIONS OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will be described indetail with reference to the accompanying drawings. Note that componentshaving the same function are denoted by the same reference symbolsthroughout the drawings for describing the present embodiment, and therepetitive description thereof will be omitted. Same members as those inthe conventional techniques (FIG. 10, FIG. 11, and FIG. 12) are attachedwith same reference numerals in principle, and description thereof isomitted.

First Embodiment

FIG. 1 is a circuit diagram showing a DC/DC converter using asystem-in-package according to a first embodiment of the presentinvention. In a DC/DC converter according to the present embodiment, asystem-in-package 1 comprises a high-side MOSFET (a high-side switch) 2,a low-side MOSFET (a low-side switch) 3, a high-side pre-driver 4 fordriving a gate of the high-side MOSFET 2, and a low pre-driver 5 fordriving a gate of the low-side MOSFET 3, where the pre-drivers 4 and 5are formed as a driver IC 6 in one chip, and three chips of thehigh-side MOSFET 2, the low-side MOSFET 3, and the driver IC 6 aremounted in one package.

Since an operation principle and respective constituent elements of aDC/DC converter using the system-in-package 1 are similar to those ofthe conventional DC/DC converter shown in FIG. 10 described above,detailed description thereof is omitted here.

A feature of the DC/DC converter of the present embodiment lies in thata reference potential for driving the low-side MOSFET 3 is not takenfrom a main circuit connecting the input capacitor 14, the high-sideMOSFET 2 and the low-side MOSFET 3 but it is taken from a logic ground30 using a wire 31. That is, a reference potential of the low-sidepre-driver 5 is applied from a portion except for the main circuitpassing through the high-side MOSFET 2 and the low-side MOSFET 3.

FIG. 2 is a diagram showing parasitic inductances in the main circuit inthe DC/DC converter according to the first embodiment. A feature of thefirst embodiment lies in that a parasitic inductance between the sourceof the low-side MOSFET 3 and the reference potential of the pre-driver 5is increased to a large value L5+L6 without increasing the sum of theparasitic inductances in the main circuit.

Here, influence of the parasitic inductance between a source of alow-side MOSFET 3 and a reference potential of a pre-driver 5 in aconventional DC/DC converter (FIG. 12) will be explained with referenceto FIGS. 14A and 14B. When the low-side MOSFET 3 is turned OFF, acurrent flows from the low-side MOSFET 3 to a built-in diode in thelow-side MOSFET 3, and the current flows in a direction shown by thearrow in FIG. 14A in the OFF-state of the low-side MOSFET 3. Here, whenthe high-side MOSFET 2 starts turning-ON, the current flowing in thebuilt-in diode in the low-side MOSFET 3 starts decreasing, so that aninduced electromotive force L5×dI/dt across both ends of the parasiticinductance L5 occurs in a direction shown in FIG. 14B. Here, since anoutput voltage of the pre-driver 5 is 0 volt, a voltage applied across agate and the source of the low-side MOSFET 3 becomes a negativepotential which is −L5×dI/dt.

FIG. 3 is a graph showing a calculation result of a voltage Vgs betweenthe gate and the source of the low-side MOSFET 3 obtained when L5 ischanged. As shown in FIG. 3, the gate voltage is changed to a negativepotential by making L5 large as shown in FIG. 3, and even if the gatevoltage thereafter rises due to the self turn-on phenomenon, the risingof the voltage can be suppressed and the self turn-on phenomenon can beprevented. Thus, when the parasitic inductance L5 is increased, negativepotential driving of the gate can be realized without providing anexternal circuit or the like, and the self turn-on can be prevented. Inthe conventional system-in-package, since the reference voltage for thepre-driver 5 is taken from the source electrode of the low-side MOSFET 3using a wire 10, L5 contains only the parasitic inductance of the sourceelectrode and it is very small.

In the first embodiment, therefore, since L6 which is a relatively largeparasitic inductance is contained in the parasitic inductance betweenthe source and the reference potential by taking the reference potentialfor the pre-driver 5 from the logic ground 30, an effect of the negativepotential drive is made large, so that self turn-on prevention can berealized. Further, when the sum of the parasitic inductances in the maincircuit is made large by making L5 large, the total loss also becomeslarge. However, the present embodiment provides a configuration whereonly the parasitic inductance between the source of the low-side MOSFET3 and the reference potential can be made large by taking the referencevoltage of the pre-driver 5 from the logic ground 30 without increasingthe sum of the parasitic inductance in the main circuit.

FIG. 4 and FIG. 5 are diagrams showing configuration examples of thesystem-in-package for realizing the first embodiment. In the driver IC 6in the conventional system-in-package (FIG. 10 and FIG. 11), thereference potential of the pre-driver 5 in the low-side MOSFET 3 is putin a floating state and the potential is fixed by connecting a pad 34 ofthe reference potential and a source pad 22 of the low-side MOSFET 3 toeach other by the wire 10. In the first embodiment, since the referencevoltage in the driver IC 5 is taken from the logic ground 30, thereference potential and the logic ground are connected to each otherusing the wire 32 in the chip inside the driver IC 6 in theconfiguration shown in FIG. 4 or using the wire 33 in the tab 17 of thelogic ground in the configuration shown in FIG. 5.

As explained above, according to the first embodiment, the self turn-onphenomenon can be prevented without increasing loss and loss reductionin the system can be achieved by taking the reference potential of thepre-driver 5 for driving the low-side MOSFET 3 from the logic ground 30using the wire 32 within the chip inside the driver IC 6 or the wire 33connected to the tab 17 of the logic ground.

Second Embodiment

FIG. 6 is a circuit diagram showing a DC/DC converter using a discretedevice according to a second embodiment of the present invention. Afeature of the second embodiment lies in that a reference voltage for apre-driver 5 is taken from a portion nearest to a ground terminal of aninput capacitor 14 through a wire 35. The second embodiment is atechnique suitable for a DC/DC converter using the conventional discretedevice instead of the system-in-package.

FIG. 7 is a diagram showing one example of a wiring pattern of a printcircuit board using the discrete device according to the secondembodiment, where the reference voltage for the pre-driver 5 is takenfrom a portion nearest to the ground terminal of the input capacitor 14through the wire 35 in the wiring pattern on the print circuit board.Conventionally, as shown in FIG. 15, the reference potential is takenfrom a portion near to the source of the low-side MOSFET 3 through thewire 10.

In FIG. 7 and FIG. 15, although connections utilizing planar wires areshown for easy understanding, an actual printed circuit board includesmulti-layered wires, where wires from the driver IC 6 are arranged so asto make connections at the shortest distances and connections are madejust below respective terminals. In the case of the discrete device, thedriver IC 6 and the PWM controller 11 are frequently constituted as onechip, where the number of pins or the shape of the package may bedifferent from those shown in FIG. 7 and FIG. 15.

As described above, according to the second embodiment, since theparasitic inductance between the source of the low-side MOSFET 3 and thereference potential of the pre-driver 5 can be made large by taking thereference potential of the pre-driver 5 from a portion nearest to theground terminal of the input capacitor 14 through the wire 35 withoutincreasing the sum of the parasitic inductances in the main circuit likethe first embodiment, the self turn-on phenomenon can be preventedwithout increasing loss and loss reduction in the system can berealized.

Third Embodiment

FIG. 8 is a circuit diagram of a DC/DC converter in which an auxiliarySchottky barrier diode is built-in according to a third embodiment. Afeature of the third embodiment lies in that a Schottky barrier diode(SBC) 36 is built-in between a gate and a source of a low-side MOSFET 3.In the present invention, since a gate voltage is changed to a negativepotential only for a moment when self turn-on occurs and an outputvoltage of a pre-driver 5 is changed to a negative potential at thistime, there is a possibility that a pn junction in a driver IC 6operates so that the pre-driver 5 causes malfunction or breaking.

A feature of the third embodiment lies in that the gate voltage isclamped at −Vf which is a forward voltage of the auxiliary SBD 36 byincorporating the auxiliary SBD 36 between the gate and the source ofthe low-side MOSFET in order to prevent the above-described malfunction.Since the forward voltage of SBD is generally low relative to a forwardvoltage at the pn junction, the malfunction of the pn junction insidethe driver IC 6 can be prevented by clamping the gate voltage at theforward voltage −Vf of the SBD.

FIG. 9 is a diagram showing one example of a sectional structure of thelow-side MOSFET 3 in which the auxiliary SBD 36 is built-in. In thethird embodiment, a structure of a vertical type MOSFET of a trench typeis shown, but the present invention can also be applied to a planar typeor a horizontal type MOSFET. In a structure of the trench type MOSFET,trench gates and channel layers 39 are formed in an n⁻ epitaxial layer38 on an n⁺ substrate 37, and polysilicon electrodes 41 are formed inthe trench gates through gate insulating films 42. P⁺ layers 43 fortaking a body contact with an n⁺ layer 44 are formed in the channellayers 39. Electrodes 46 made of aluminum are formed on a surface andthe electrodes 46 are separated from one another by thick insulatingfilms 45. The SBD is formed at a device peripheral portion and, the p⁺layer 43 and a Schottky junction 47 are formed in a deep p-type welllayer 40 for obtaining peripheral withstand voltage.

The auxiliary SBD 36 can be easily built-in for forming the presentdevice by only adding a photo process for obtaining the Schottkyjunction 47.

As described above, according to the third embodiment, the self turn-onphenomenon can be prevented and loss reduction in the system can berealized like the first embodiment without increasing loss, andmalfunction or breaking of the pre-driver 5 can be further prevented byincorporating the auxiliary SBD 36 between the gate and the source ofthe low-side MOSFET 3.

In the foregoing, the invention made by the inventors of the presentinvention has been concretely described based on the embodiments.However, it is needless to say that the present invention is not limitedto the foregoing embodiments and various modifications and alterationscan be made within the scope of the present invention.

The present invention relates to a technique for a non-isolated DC/DCconverter, and it can be utilized in a circuit system or a mountingsystem which is used in a system-in-package or a discrete device andwhich can prevent the self turn-on phenomenon without newly adding anymember or changing a drive system.

1. A non-isolated DC/DC converter comprising: a high-side switch; alow-side switch; a high-side pre-driver which drives the high-sideswitch; and a low-side pre-driver which drives the low-side switch,wherein a reference potential for the low-side pre-driver which drivesthe low-side switch is applied from a portion except for a main circuitpassing through the high-side switch and the low-side switch.
 2. TheDC/DC converter according to claim 1, wherein the reference potentialfor the low-side pre-driver is applied from a logic ground.
 3. Anon-isolated DC/DC converter using a system-in-package constituted witha high-side switch; a low-side switch; and a driver IC obtained byforming a high-side pre-driver which drives the high-side switch and alow-side pre-driver which drives the low-side switch in one chip,wherein a reference potential for the low-side pre-driver which drivesthe low-side switch is applied from a portion except for a main circuitpassing through the high-side switch and the low-side switch.
 4. TheDC/DC converter according to claim 3, wherein the reference potentialfor the low-side pre-driver is applied from a logic ground.
 5. The DC/DCconverter according to claim 4, wherein the reference potential for thelow-side pre-driver is applied from a logic ground connected thereto viaa wiring inside the driver IC.
 6. The DC/DC converter according to claim4, wherein the reference potential for the low-side pre-driver isapplied from a logic ground connected thereto by connecting thereference potential and a tab mounted with the driver IC with wirebonding.
 7. A non-isolated DC/DC converter comprising: a high-sideswitch; a low-side switch; a high-side pre-driver which drives thehigh-side switch; and a low-side pre-driver which drives the low-sideswitch, wherein a reference potential for the low-side pre-driver whichdrives a gate of the low-side switch is applied from a portion nearestto a ground terminal of an input capacitor through a wiring pattern on aprinted circuit board.
 8. The DC/DC converter according to claim 1,wherein a Schottky barrier diode is connected between a gate and asource of the low-side switch.
 9. The DC/DC converter according to claim3, wherein a Schottky barrier diode is connected between a gate and asource of the low-side switch.
 10. The DC/DC converter according toclaim 7, wherein a Schottky barrier diode is connected between a gateand a source of the low-side switch.
 11. The DC/DC converter accordingto claim 8, wherein the Schottky barrier diode is built-in in a chip onwhich the low-side switch is disposed.
 12. The DC/DC converter accordingto claim 9, wherein the Schottky barrier diode is built-in in a chip onwhich the low-side switch is disposed.
 13. The DC/DC converter accordingto claim 10, wherein the Schottky barrier diode is built-in in a chip onwhich the low-side switch is disposed.
 14. The DC/DC converter accordingto claim 1, wherein the high-side switch and the low-side switch eachcomprises a power MOSFET.
 15. The DC/DC converter according to claim 3,wherein the high-side switch and the low-side switch each comprises apower MOSFET.
 16. The DC/DC converter according to claim 7, wherein thehigh-side switch and the low-side switch each comprises a power MOSFET.